Hydraulic apparatus



Feb. 14, 1967 A. G. HUTCHEON 3,303,648

HYDRAULIC APPARATUS Filed June 16, 1965 2 ee s-S t l Iuv EMTOE lI/cr: au/er Q, H d/c waq 8v l w-roe u av Feb. 14, 1967 A. G. HUTCHEON 3,303,648

HYDRAULIC APPARATUS Filed June 16, 1965 2 Sheets-Sh et 2 fl ewder 6. Menu 5v @QMM M A-r-roeuEY United States Patent Cfifice 3,363,648 Patented Feb. 14, 1967 3,303,648 HYDRAULIC APPARATUS Alexander G. Hutcheon, Benhall, Cheltcnham, England, assignor to Dowty Technical Developments Limited, Brockhampton, Cheltenham, England, a British com- Filed June 16, 1965, Ser. No. 464,349 Claims priority, application Great Britain, June 17, 1964, 25,205/64 2 Claims. (CI. 6053) This invention relates to hydraulic apparatus and more particularly to a hydraulic power transmission which comprises a variable positive displacement hydraulic pump in hydraulic connection with a variable positive displacement hydraulic motor, the pump being adapted to receive power from a power source and the motor being adapted to deliver power to a load, the speed ratio between the motor speed and the pump speed being determined by the relative displacements of the pump and the motor.

In the Specification the term displacement as applied to a hydraulic pump or to a hydraulic motor refers to the volumetric liquid displacement per revolution of the pump or the motor.-

In accordance with the present invention a hydraulic power transmission includes a linkage means to interconnect the displacement varying means of the pump and the motor so that the pump and the motor displacements are simultaneously variable to vary the transmission speed ratio wherein the linkage means is arranged to enter -a dead centre position having regard to the pump displacement varying means to determine the maximum motor displacement setting and wherein the range of adjustment includes a position in which the motor has zero displacement.

The pump and/ or the motor may be of the tilting head kind which comprises a rotary member secured to a drive shaft at a head tiltable about a tilt axis relatively to the rotary member. The head comprises a frame or casing containing a rotary cylinder block, a rotary drive means between the rotary member and the cylinder block and pistons associated with the cylinder block to reciprocate during rotation of the rotary member. The tilt angle of the head relatively to the rotation axis of the rotary member determines the effective stroke of the pistons in their cylinders and thus determines the displacement of the unit. A pump or motor of this kind set forth in this paragraph will, for convenience, be referred to hereafter as a tilting head pump unit or a tilting head motor unit.

Where the transmission comprises a tilting head pump unit and a tilting head motor unit the linkage means may comprise a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and to the motor head. The provision to give both forward and reverse speeds may comprise arranging that the pump in its range of displacement adjustment moves smoothly from forward to reverse displacement and vice versa through a Zero displacement condition.

A removable stop may act normally to prevent the motor head from moving to its Zero displacement position but which is removable under manual control when it is desired to move the motor head to zero displacement.

The motor displacement varying mechanism may pass through a dead centre position relative to the link in order to reach the Zero displacement condition.

The removable stop may form part of an adjusting means adapted to engage the motor head to move it through its dead centre position to a zero displacement position.

A fixed stop may determine the limit of movement of the motor head at the motor zero displacement position.

The advantage gained by arranging in a transmission that the motor may be moved to a zero displacement position is that the output shaft from the transmission may then rotate quite freely without substantial restrictions from the transmission. used for propelling a vehicle the moving of the motor to zero displacement will enable the vehicle either to coast or to be towed without any substantial resistance to movement from the transmission.

How the invention can be carried into effect is hereinafter particularly described with reference to the accompanying drawings in which,

FIGURES 1, 2, 3 and 4 diagrammatically illustrate the transmission in different positions,

FIGURE 5 is a cross section of the transmission of FIGURES 1 to 4 arranged in its reservoir casing, and

FIGURE 6 is a cross section through the pump employed in FIGURES 1 to 5.v

The transmission illustrated in FIGURES 1 to 5 comprises a tilting head pump 1 and a tilting head motor 2 which are hydraulically interconnected by hydraulic passages. Both the pump and the motor are tilting head units and before proceeding further with the description of FIGURES 1 to 5 reference is made to FIGURE 6 which illustrates the structure of a typical tilting head pump unit, for example the pump 1 of FIGURES l to 5. A rotary drive shaft 3 is suitably mounted for rotation within a fixed bearing housing 31 and a tilting head 4 is mounted in trunnions 5 for tilting movement about an axis extending perpendicularly to the axis of the drive shaft 3. The drive shaft 3 is integrally formed with a drive flange 32 which bears against a thrust bearing surface 33 formed on the housing 31. The trunnions 5 are formed one on either side of the housing 31, these trunnions being engaged by the arms 34 of a yoke 4. It will be understood that the yoke includes a pair of arms 34 disposed one on either side of the drive flange 33. The base 35 of the yoke 4 comprises a valve plate on which a cylinder block 36 is mounted for rotation. The cylinder block 36 is located in position on the valve plate by means of a fixed axle 37 secured to the valve plate. Within the cylinder block 36 a number of cylinders 38 are formed whose axes extend parallel to the axis of block rotation. These cylinders are open at the end of the cylinder block facing the drive flange 32. The end of the cylinder block which co-operates with the valve plate 35 is formed with a number of cylinder ports 39 which extend one from each cylinder 38. The ports 39 co-operate with a pair of fixed ports 41 and 42 in the valve plate. Within each cylinder 38 a piston 43 is slidably mounted. Each piston is hollow and includes a connecting rod 44 secured within the hollow portion and capable of limited angular movement within the piston. The connecting rods 44 extend from the pistons and terminate in ball joints 45. Each ball joint 45 is located within a socket member 46 fixed in the drive flange 32. The yoke 4 and the cylinder block 36 are pivotally mounted at the trunnions 5 to be capable of angular movement about the trunnion axis which is arranged to pass diametrically through the drive flange 32 through a circle on which the centres of the ball joints 45 are located. Assuming that the yoke is so positioned that the rotation axes of the cylinder block 36 and the drive shaft 3 are inclined to one another it will be seen that rotation of the drive shaft and rotation of the cylinder block will cause reciprocation of the pistons 43 within cylinders 38, one complete reciprocation of each piston being effected for each complete revolution of the drive shaft 3. The ports 41 and 42 are so positioned that by rotation of the drive shaft 3 liquid is displaced from one of the ports 41 or 42 and delivered at the other port 41 Where the transmission is or 42. Rotational drive of the cylinder block is obtained by virtue of the fact that the connecting rods 44 engage the interior surfaces of their associated pistons 43. The stroke of the pistons 43 within their cylinders is determined by the angular inclination of the rotation axis of the cylinder block to the rotation axis of the drive shaft 3, the greater the inclination, the greater the stroke. At the position where the axes of the cylinder block 36 and of the drive shaft 3 are aligned the pistons will have no stroke.

Extending from the yoke 4 is a lug 48 at the end of which a pair of swivel joints 11 are located. From the swivel joints 11 a pair of parallel links 9 extends to the corresponding swivel joints 12 of the tilting head motor unit of the transmission. In FIGURES 1 to 4 the two parallel links 9 are indicated as a single link 9. The two parallel links perform the hydraulic function of carrying flow and return liquid in between the two tilting head units for the transmission of power from the pump drive shaft to the motor drive shaft. The links also perform a mechanical function in that they link together the pump and the motor heads 4 and 7 for simultaneous displacement adjustment movement.

FIGURES l, 2, 3 and 4 diagrammatically illustrate the transmission in differing positions. In this embodiment the transmission comprises a tilting head pump 1 constructed substantially as described with reference to FIGURE 6 and a tilting head motor 2 also constructed substantially as shown in FIGURE 6. The pump and the motor are hydraulically interconnected by the passages formed within the links 9 although it is within the the scope of the invention to use any other known form of hydraulic connection between the pump and the motor. For adjustment of the speed ratio of the transmission a servo motor comprising a servo piston 13 slidable within a servo cylinder 14 is provided. Piston rod 15 extends from the piston 13 and from its outer end a pivoted link 16 extends to a lever 17 projecting from the side of the pump head 4. The servo piston 13 may be adjusted by servo pressure under any conventional control for selecting speed ratio of the transmission.

The transmission as described is mounted in a support or casing 49 (see FIGURE 5) in which the bearing housings 31 and 51 for the pump and the motor shafts 3 and 6 are fixedly mounted. The trunnions 5 and 8 of the pump and the motor are also fixedly mounted within the casing to the respective bearing housings. For the pump head 4 a lever arm is formed by the head between the hinge 11 and the trunnion 5 and for the motor head 7 a lever arm is formed by the head between the hinge 12 and the trunnion 8. The motor head, the pump head, the link and the casing 49 which supports the trunnions 5 and 8, effectively form a quadrilateral linkage or a four-bar chain which is adjustable into different forms by a pivotal movement of the heads 4 and 7 about the trunnions. In the embodiment illustrated in FIGURES 1 to 5 the lever arms formed by the pump head and by the motor head are equal in length to the length of the link 9 whilst the spacing maintained by the casing between the trunnions 5 and 8 is somewhat less than three times the length of the link 9.

In one position of the transmission as illustrated in FIGURE 1 it will be seen that the hinges 11 and 12 and the trunnion 5 lie in one plane. This position is referred to as the pump dead centre position. In this position the hinge 12 is disposed at the greatest possible distance from the trunnion 5 and determines the maximum angular movement of the motor head 7 relative to its drive shaft 6 which in turn corresponds to the maximum hydraulic displacement of the motor. In the pump dead centre position shown in FIGURE 1 it is also arranged that the pump head 4 has a zero tilt angle about its trunnions 5 so that the cylinder barrel within the head 4 is aligned with the drive shaft 3. In this condition the hydraulic displacement of the pump is zero.

Thus as shown in FIGURE 1 rotation of the drive shaft 3 will displace no liquid from the pump 1 and accordingly the motor drive shaft 6 will not rotate. FIGURE 2 shows the transmission of FIGURE 1 when adjusted for maximum forward speed ratio. The servo piston 13 has been moved to cause a maximum clockwise movement of the pump head 4 to give a maximum displacement to the pump. This maximum movement of the pump head 4 will, through the medium of the link 9, have moved the motor head towards its zero displacement position holding the motor at a small displacement. In this condition the speed ratio between the pump and the motor drive shafts is at a maximum value in the forward direction.

In FIGURE 3 the pump head 4 has been moved to a position to obtain maximum reverse speed ratio and for this purpose the servo piston 13 has moved towards its opposite extremity to cause anti-clockwise movement of the pump head 4. This displacement of the pump is now reversed having regard to its displacement of FIGURE 2 and liquid will be delivered to the motor in the reverse direction. The displacement of the motor 2 in FIGURE 3 is substantially the same as that shown in FIGURE 2, i.e. it is reduced from its maximum value but has not reached a zero value. The speed ratio therefore in FIG- URE 3 between the pump drive shaft and the motor drive shaft is at a maximum value in the reverse direction.

Within the casing 49 a rotary shaft 18 is mounted in fixed bearings and is angularly adjustable by means of a manual lever 19. Within the casing or support a stop, formed on a manual lever 21, extends from the shaft 18 towards a connecting rod 15 from the servo piston 13. In the zero and forward speed ratio conditions of FIGURES 1 and 2 the two free ends of the lever 2 and the connecting rod 15 are spaced apart. However in FIGURE 3 representing maximum reverse speed ratio, the free end of the connecting rod 15 makes contact with the free end of lever 21 and the lever 21 thereby forms a stop determining a normal maximum reverse speed ratio of the transmission.

Also extending from the shafts 18 is a catch plate 22 having at its free end a recess 23. The recess 23 is so positioned that when lever 19 is in the position shown in any of FIGURES 1, 2 and 3, a projection 24 from the pump head will move into the recess 23 at the maximum forward or reverse speed ratio conditions of the transmission. If it is desired that the vehicle be towed or permitted to coast, lever 19 is moved in a clockwise direction into a position shown in FIGURE 4. Such movement will initially remove the lever 21 from engagement with the connecting rod 15 and secondly will cause recess 23 and catch plate 22 to engage the projection 24 of the motor head to urge the motor head towards a zero displacement position. A suitable fixed stop 25 carried by the support or casing holds the motor head at its zero displacement position.

In movement of the transmission from the FIGURE 3 position to the FIGURE 4 posit-ion the pump head will initially move slightly beyond its maximum reverse displacement until the link 9 is in a dead centre position having regard to the motor head. As the motor head moves beyond this dead centre position the pump head 4 will be moved by the link 9 to a position of slightly smaller reverse displacement. The location of the motor at zero displacement in the FIGURE 4 position means that the wheels of the vehicle driven by the motor drive shaft 6 can rotate freely with substantially no resistance to motion from the transmission. The vehicle may then be towed or may coast since rotation of the motor drive shaft involves no displacement of liquid from the motor.

The reseroir casing 49 is arranged to contain the working liquid of the transmission and in practice the level of the liquid is such as to cover entirely or almost entirely the motor head 7 and the portion of the motor shaft bearing housing 51 within the reservoir casing 49. Thus although rotation of the motor shaft 6 involves rotation of the motor cylinder barrel on the motor valve plate the fact that the motor head is immersed in the working liquid will ensure adequate lubrication.

When it is desired to restore the vehicle to its self propelling condition, the lever 19 is moved back to the position shown in FIGURES 1, 2 or 3. Such movement will cause the catch plate 22 to move the motor head from its zero displacement position through a dead centre position having regard to the link 9 onto it maximum displacement position as shown in FIGURE 3. The servo piston 13 can now exercise control over both the pump and the motor to adjust transmission speed ratio between the limits shown in FIGURES 2 and 3. It will be appreciated that before the servo piston 13 can take control of the transmission the catch plate 22 must move the motor head through its dead centre position having regard to the link, otherwise movement of the servo piston would merely cause the link to push the motor head 7 back against the fixed stop 25.

I claim as my invention:

1. A hydraulic power transmission comprising a variable positive displacement hydraulic pump, a variable positive displacement hydraulic motor hydraulically connected to the pump, linkage means arranged to adjust the pump and motor displacements simultaneously, to vary the speed ratio of the transmission, and stop means arranged to locate the motor in a zero displacement position', the pump and mot-or being of the tilting head type and the linkage means being connected between the tilting heads of the pump and the motor, and comprising a pivot on the pump head, a pivot on the motor head, and a link of fixed length extending between the two pivots and arranged to pass through a zero displacement position relatively to the motor head, to reach the zero displacement position of the motor, there being a removable stop adapted to engage the motor head at a position near its dead centre relative to the link, so as normally to prevent the motor head from passing through its dead centre to the zero displacement position.

2. A hydraulic power transmission as claimed in claim 1 including adjusting means associated with the removable stop for engaging the motor head near its dead centre relative to the link to urge the motor head through the dead centre position to engage the fixed stop at the zero position.

References Cited by the Examiner UNITED STATES PATENTS 3,052,098 9/1962 Ebert 53 3,142,963 8/1964 Thoma 60-53 3,143,859 8/1964 Thoma -a 6053 EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A HYDRAULIC POWER TRANSMISSION COMPRISING A VARIABLE POSITIVE DISPLACEMENT HYDRAULIC PUMP, A VARIABLE POSITIVE DISPLACEMENT HYDRAULIC MOTOR HYDRAULICALLY CONNECTED TO THE PUMP, LINKAGE MEANS ARRANGED TO ADJUST THE PUMP AND MOTOR DISPLACEMENTS SIMULTANEOUSLY, TO VARY THE SPEED RATIO OF THE TRANSMISSION, AND STOP MEANS ARRANGED TO LOCATE THE MOTOR IN A ZERO DISPLACEMENT POSITION, THE PUMP AND MOTOR BEING OF THE TILTING HEAD TYPE AND THE LINKAGE MEANS BEING CONNECTED BETWEEN THE TILTING HEADS OF THE PUMP AND THE MOTOR, AND COMPRISING A PIVOT ON THE PUMP HEAD, A PIVOT ON THE MOTOR HEAD, AND A 